The study, published in the journal, Pediatrics, analyzed more than 20 million births, including more than 19,000 unexpected infant deaths. It found that the risk of death rises ever so slightly for each additional cigarette a pregnant woman smokes.

Not only that, but researchers say if the woman smokes a pack a day while pregnant, the baby's risk of unexpected sudden death nearly triples compared to the infants of non-smokers.

According to experts, self-reported statistics show that about 338,000 women admit to smoking during pregnancy each year and that more than half of them are unwilling or unable to stop.